Quote:
Originally Posted by David1912
Thanks....we would be thinking of getting by from say 7 pm through the next morning.....tv, led lights, possibly small fan, coffee grinder and coffee maker in morning....possibly microwave for 2 minutes....
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I would worry about the coffee maker and microwave the most. That's a lot different than TVs, small fans, or LED lights. I'm not familiar with power requirements of coffeee grinders, although I expect they are not as high or used as long.
Anyway, based on minimal research I've done to engineer the system I want, it appears there is significant variation in how some flooded batteries handle high current requirements. While I hardly take everything I read on internet as gospel, there seems to be general agreement that the Peukert number has a wide range of values for flooded batteries.
In the graph below used as an example (let's assume it's accurate), a 120 Amp-hour battery can be reduced to as low as 20 Amp-hours, and that's at only 50 Amps or so. If taken up to 120 Amps (the equivalent of taking two 80 Amp-hour batteries to at least 80 Amps each to power a 2,000-watt inverter under heavy load), then we may see much less than even 20 Amp-hours; and that's from a battery rated at 120 Amp-hours. It's possible that in some applications the battery bank may only be able to provide 10% or so of rated capacity.
This is why increasing battery capacity can be so important -- not only do we start with more Amp-hours, but the specific discharge rate will be much lower, thereby allowing batteries to deliver a greater percentage of their rated capacity (which is at a very slow 20-hour rate, not extremely fast 4-minute rate).
Chart context is from this site:
BU-503: How to Calculate Battery Runtime – Battery University
By the way, since you mentioned going to AGM batteries, I suspect you already knew most of this. I'm posting in case it helps others who kill their batteries much faster than they expected and can't figure out why.
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